1. Field of the Invention
The present invention relates to a vehicle occupant restraint and, in particular, to a pretensioner for taking up slack in a seat belt in the event of a vehicle collision.
2. Description of the Prior Art
U.S Pat. No. 4,178,016 discloses a vehicle seat belt pretensioner which is activated by ignition of a pyrotechnical charge. The pyrotechnical charge is ignited by a fuse which is connected to the pyrotechnical charge.
U.S. Pat. No. 4,549,704 also discloses a seat belt pretensioner. The seat belt is wound on the spool of a seat belt retractor. The pretensioner comprises a tension roll which is mounted on an axial extension of the shaft for the retractor spool. A cable is looped around the tension roll several times. The tension roll can rotate within the cable wraps without frictionally engaging the cable during normal withdrawal and retraction of the seat belt. A free end of the cable is attached to a drive device. The drive device is movable in a direction away from the tension roll. When moved, a loop of the cable is contracted onto the tension roll. Further movement of the drive device rotates the tension roll, in turn, rotating the seat belt spool in a belt retraction direction. The number of loops of the cable on the tension roll is sufficient to pull the seat belt against the occupant and eliminate any slack in the seat belt webbing.
U.S. Pat. No. 4,789,185 discloses a gas generator for actuating a drive device for a seat belt pretensioner. The gas generator comprises a housing containing a propellant charge. A piston is connected to a free end of a pretensioner take-up device such as that disclosed in U.S. Pat. No. 4,549,704. On ignition, the propellant charge generates a high pressure gas which acts against the piston causing the pretensioner to rotate a seat belt spool in a belt retraction direction.
Other patents which disclose seat belt pretensioning devices are U.S. Pat. No. 4,750,686; U.S. Pat. No. 4,573,322; and U.S. Pat. No. 4,750,685.
U.S. Pat. No. 4,706,990 discloses a detonation train for actuation of a gas generator for a vehicle occupant airbag restraint. The detonation train comprises a fuse which is capable of transferring an initiation stimulus received from an impact sensor. The fuse can be a mild detonating fuse (MDF) or a thin layer explosive line (TLX). The fuse contains a pyrotechnic material and has a high rate of propagation, e.g., 6,000-21,000 feet per minute. The fuse ignites an ignition material. The patent discloses, as suitable ignition materials, HAVELITE (trademark, McCormick Selph Associates) and ITLX (trademark, Explosive Technologies, Inc.).